The Supreme Court said Tuesday investigators don't have to read Miranda rights to inmates during jailhouse interrogations about crimes unrelated to their current incarceration.

The high court, on a 6-3 vote, overturned a federal appeals court decision throwing out prison inmate Randall Lee Fields' conviction, saying Fields was not in "custody" as defined by Miranda and therefore did not have to have his rights read to him.

"Imprisonment alone is not enough to create a custodial situation within the meaning of Miranda," Justice Samuel Alito wrote in the court's majority opinion.

Three justices, Ruth Bader Ginsburg, Stephen Breyer and Sonia Sotomayor, dissented and said the court's decision would limit the rights of prisoners.

"Today, for people already in prison, the court finds it adequate for the police to say: 'You are free to terminate this interrogation and return to your cell,'" Ginsburg said in her dissent. "Such a statement is no substitute for one ensuring that an individual is aware of his rights."

Miranda rights come from a 1966 decision that involved police questioning of Ernesto Miranda in a rape and kidnapping case in Phoenix. It required officers to tell suspects they have the right to remain silent and to have a lawyer represent them, even if they can't afford one.

Previous court rulings have required Miranda warnings before police interrogations for people who are in custody, which is defined as when a reasonable person would think he cannot end the questioning and leave.